Naming Saturated Hydrocarbons • The International Union of Pure and Applied Chemistry (IUPAC) names for the first 12 "straight-chain" or "normal" alkanes are:
Alkanes and Cycloalkanes • The simplest saturated hydrocarbons are called alkanes. • Methane, CH4, is the simplest alkane. • The alkanes form a homologous series. • Each member of the series differs by a specific number and kind of atoms.
Alkanes and Cycloalkanes • The alkanes differ from each other by a CH2 or methylene group. • All alkanes have this general formula. CnH2n+2 • For example ethane, C2H6 , and propane, C3H8 , are the next two family members.
Alkanes and Cycloalkanes • Isomers are chemical compounds that have the same molecular formulas but different structures. • Two alkanes have the molecular formula C4H10. • They are a specific type of isomer called structural isomers. • Branched-chain alkanes are named by the following rules.
Naming Saturated Hydrocarbons • Choose the longest continuous chain of carbon atoms which gives the basic name or stem. • Number each carbon atom in the basic chain, starting at the end that gives the lowest number to the first group attached to the main chain (substituent). • For each substituent on the chain, we indicate the position in the chain (by an Arabic numeric prefix) and the kind of substituent (by its name). • The position of a substituent on the chain is indicated by the lowest number possible. The number precedes the name of the substituent. • When there are two or more substituents of a given kind, use prefixes to indicate the number of substituents. • di = 2, tri = 3, tetra = 4, penta = 5, hexa = 6, hepta = 7, octa = 8, and so on. • The combined substituent numbers and names serve as a prefix for the basic hydrocarbon name. • Separate numbers from numbers by commas and numbers from words by hyphens. • Words are "run together".
Naming Saturated Hydrocarbons • Alkyl groups (represented by the symbol R) are common substituents. • Alkyl groups are fragments of alkanes in which one H atom has been removed for the connection to the main chain. • Alkyl groups have the general formula CnH2n+1. • In alkyl groups the -ane suffix in the name of the parent alkane is replaced by -yl. • A one carbon group is named methyl. • A two carbon group is named ethyl. • A three carbon group is named propyl. • Three alkanes have the formula C5H12. • There are three structural isomers of pentane.
Alkanes and Cycloalkanes • There are five isomeric hexanes, C6H14. • The number of structural isomers increases rapidly with • increasing numbers of carbon atoms. • The boiling points of the alkanes increase with molecular weight.
Alkanes and Cycloalkanes • Cyclic saturated hydrocarbons are called cycloalkanes. • They have the general formula CnH2n. • Some examples are:
Alkenes • The three classes of unsaturated hydrocarbons are: • alkenes and cycloalkenes, CnH2n • alkynes and cycloalkynes, CnH2n-2 • aromatic hydrocarbons • The simplest alkenes contain one C=C bond per molecule. • The general formula for simple alkenes is CnH2n. • The first two alkenes are: • ethene, C2H4 • and propene, C3H6 • Each doubly bonded C atom is sp2 hybridized. • The sp2 hybrid consists of: • two s bonds (single bonds) and • one s and one p bond (double bond)
Alkenes • The systematic naming system for alkenes uses the same stems as alkanes. • In the IUPAC system, the -ane suffix for alkanes is changed to -ene. • Common names for the alkenes have the same stem but use the suffix -ylene is used. • In chains of four or more C atoms, a numerical prefix shows the position of the lowest-numbered doubly bonded C atom. • Always choose the longest chain that contains the C=C bond. • Polyenes contain two or more double bonds per molecule. • Indicate the number of double bonds with suffixes: • -adiene for two double bonds. • -atriene for three double bonds, etc. • The positions of the substituents are indicated as for alkanes. • The position of the C=C bond(s) is/are given the lowest number(s) possible.
Cycloalkenes • Cycloalkenes have the general formula CnH2n-2. • Examples are: • cyclopentene • cyclohexene
Alkynes • Alkynes contain CC bonds. • The simplest alkyne is C2H2, ethyne, or acetylene. • Alkynes with only one C C bond have the formula CnH2n-2. • Each carbon atom in a C C bond is sp hybridized. • Each sp hybrid contains two bonds and two bonds. • The carbon atom will have one single bond and one triple bond. • Alkynes are named like the alkenes except that the suffix -yne is used with the characteristic stem • The alkyne stem is derived from the name of the alkane with the same number of carbon atoms.
Aromatic Hydrocarbons • Historically, aromatic was used to describe pleasant smelling substances. • Now it refers to benzene, C6H6,and derivatives of benzene. • Other compounds that have similar chemical properties to benzene are also called aromatic. • The structure of benzene, C6H6, is: • Coal tar is the common source of benzene and many other aromatic compounds. • Some aromatic hydrocarbons that • contain fused rings are: • napthalene
Resonance in Benzene • C6H6 has two resonance structures with alternating double bonds. • The π electrons are delocalized over the ring. • C–C single bond = 154 pm • C=C bond = 134 pm • CC bonds in benzene = 139 pm π electrons delocalized
Other Aromatic Hydrocarbons • Many aromatic hydrocarbons contain alkyl groups attached to benzene rings (as well as to other aromatic rings). • The positions of the substituents on benzene rings are indicated by the prefixes: • ortho- (o-) for substituents on adjacent C atoms • meta- (m-) for substituents on C atoms 1 and 3 • para- (p-) for substituents on C atoms 1 and 4
Organic Halides • A halogen atom may replace almost any hydrogen atom in a hydrocarbon. • The functional group is the halide (-X) group. • Examples include: • chloroform, CHCl3 • 1,2-dichloroethane, ClCH2CH2Cl • para-dichlorobenzene
Alcohols and Phenols • The functional group in alcohols and phenols is the hydroxyl (-OH) group. • Alcohols and phenols can be considered derivatives of hydrocarbons in which one or more H atoms have been replaced by -OH groups. • Phenols are derivatives of benzene in which one H has been replaced by replaced by -OH group. • The stem for the parent hydrocarbon plus an -ol suffix is the systematic name for an alcohol. • A numeric prefix indicates the position of the -OH group in alcohols with three or more C atoms. • Common names are the name of the appropriate alkyl group plus alcohol.
Alcohols and Phenols • Ethyl alcohol (ethanol), C2H5OH, is the most familiar alcohol. H H O H H C C H H • Phenol, C6H5OH, is the most familiar phenol.
Alcohols and Phenols • Alcohols can be classified into three classes: • Primary (1°) alcohols like ethanol have the -OH group attached to a C atom that has one bond to another C atom. • Secondary(2°) alcohols have the –OH group attached to a C atom that has bonds to 2 other C atoms. • For example,2-propanol: • Tertiary (3°) alcohols have the –OH group attached to a C atom that is bonded to 3 other C atoms. • For example, 2-methyl-2-propanol
Alcohols and Phenols • Alcohols are named using the stem for the parent hydrocarbon plus an -ol suffix in the systematic nomenclature. • A numeric prefix indicates the position of the -OH group in alcohols with three or more C atoms. • Common alcohol names are the name of the appropriate alkyl group plus the word alcohol.
Alcohols and Phenols • There are several isomeric monohydric acyclic (contains no rings) alcohols that contain more than three C atoms. • There are four isomeric four-carbon alcohols.
Alcohols and Phenols • There are eight isomeric five-carbon alcohols.
Alcohols and Phenols • Polyhydric alcohols contain more than one -OH group per molecule.
Alcohols and Phenols • Phenols are usually called by their common (trivial) names.
Ethers • Ethers may be thought of as derivatives of water in which both H atoms have been replaced by alkyl or aryl groups. • Ethers are not very polar and not very reactive. • They are excellent solvents. • Common names are used for most ethers.
Aldehydes and Ketones • The functional group in aldehydes and ketones is the carbonyl group.
Aldehydes and Ketones • Except for formaldehyde, aldehydes have one H atom and one organic group bonded to a carbonyl group. • Ketones have two organic groups bonded to a carbonyl group.
Aldehydes and Ketones • Common names for aldehydes are derived from the name of the acid with the same number of C atoms. • IUPAC names are derived from the parent hydrocarbon name by replacing -e with -al.
Aldehydes and Ketones • The IUPAC name for a ketone is the characteristic stem for the parent hydrocarbon plus the suffix -one. • A numeric prefix indicates the position of the carbonyl group in a chain or on a ring.
Amines • Amines are derivatives of ammonia in which one or more H atoms have been replaced by organic groups (aliphatic or aromatic or a mixture of both). • There are three classes of amines.
Carboxylic acids contain the carboxyl functional group. The general formula for carboxylic acids is: R represents an alkyl or an aryl group Carboxylic Acids • IUPAC names for a carboxylic acid are derived from the name of the parent hydrocarbon. • The final -e is dropped from the name of the parent hydrocarbon • The suffix -oic is added followed by the word acid. • Many organic acids are called by their common (trivial) names which are derived from Greek or Latin.
Carboxylic Acids • Positions of substituents on carboxylic acid chains are indicated by numeric prefixes as in other compounds • Begin the counting scheme from the carboxyl group carbon atom. • They are also often indicated by lower case Greek letters. • = 1st C atom • = 2nd C atom • = 3rd C atom, etc.
Nomenclature of Carboxylic Acids • Dicarboxylic acids contain two carboxyl groups per molecule.
Carboxylic Acids • Aromatic acids are usually called by their common names. • Sometimes, they are named as derivatives of benzoic acid which is considered to be the "parent" aromatic acid.
Alcohols and Phenols • The stem for the parent hydrocarbon plus an -ol suffix is the systematic name for an alcohol. • A numeric prefix indicates the position of the -OH group in alcohols with three or more C atoms. • Common names are the name of the appropriate alkyl group plus alcohol. Ethers • Common names are used for most ethers. Aldehydes and Ketones • Common names for aldehydes are derived from the name of the acid with the same number of C atoms. • IUPAC names are derived from the parent hydrocarbon name by replacing -e with -al. • The IUPAC name for a ketone is the characteristic stem for the parent hydrocarbon plus the suffix -one. • A numeric prefix indicates the position of the carbonyl group in a chain or on a ring. Amines • Amines are derivatives of ammonia in which one or more H atoms have been replaced by organic groups (aliphatic or aromatic or a mixture of both). • There are three classes of amines. Carboxylic Acids • IUPAC names for a carboxylic acid are derived from the name of the parent hydrocarbon. • The final -e is dropped from the name of the parent hydrocarbon • The suffix -oic is added followed by the word acid. • Many organic acids are called by their common (trivial) names which are derived from Greek or Latin.
When compounds contain more than one functional group, the order of precedence determines which groups are named with prefix or suffix forms. The highest precedence group takes the suffix, with all others taking the prefix form. However, double and triple bonds only take suffix form (-en and -yn) and are used with other suffixes.
Isomerism • Isomers have identical composition but different structures • Two forms of isomerism • Constitutional (or structural) • Stereoisomerism • Constitutional • Same empirical formula but different atom-to-atom connections • Stereoisomerism • Same atom-to-atom connections but different arrangement in space. • Geometric - Geometric isomers can occur when there is a C=C double bond. • Optical - Optical isomers are molecules with non-superimposable mirror images. Such molecules are called CHIRAL. Pairs of chiral molecules are enantiomers. Chiral molecules in solution can rotate the plane of plane polarized light.
Cis-2-butene Trans-2-butene Stereoisomers: Geometric Geometric isomers can occur when there is a C=C double bond.
Stereoisomers: Optical • Optical isomers are molecules with non-superimposable mirror images. • Such molecules are called CHIRAL • Pairs of chiral molecules are enantiomers. • Chiral molecules in solution can rotate the plane of plane polarized light. • Chirality generally occurs when a C atom has 4 different groups attached. Lactic acid
Chirality: Handedness in Nature These molecules are non-superimposable mirror images.
Sugars: Related to Alcohols • Sugars are carbohydrates, compounds with the formula Cx(H2O)y. What is the difference between a and b D-glucose? Glycosidic bonds: The anomeric hydroxyl group (axial) and a hydroxyl group of another sugar or some other compound can join together, splitting out water to form a glycosidic bond. R-OH + HO-R'-->R-O-R' +H2O
Monosaccharides - simple sugars, with multiple hydroxyl groups. Based on the number of carbons (e.g., 3, 4, 5, or 6) a monosaccharide is a triose, tetrose, pentose, or hexose, etc. Disaccharides - two monosaccharides covalently linked Oligosaccharides - a few monosaccharides covalently linked. Polysaccharides - polymers consisting of chains of monosaccharide or disaccharide units
Deoxyribose, the sugar in the DNA backbone. Sucrose and Ribose Sucrose, common table sugar, has a glycosidic bond linking the anomeric hydroxyls of glucose and fructose. Because the configuration at the anomeric carbon of glucose is a (O points down from the ring), the linkage is designated a(1®2). The full name is a-D-glucopyranosyl-(1®2)b-D- fructopyranose.